1. Field of the Invention
The present invention relates to an active matrix type liquid crystal display (referred to as active matrix type LCD hereinafter) which employs metal-insulator-metal (referred to as MIM hereinafter) elements, and more particularly, to an MIM type active matrix LCD (referred to as MIM-LCD hereinafter) free from image sticking.
2. Description of the Related Art
As the past examples of LCDs that employs MIMs, there may be mentioned those disclosed in D. R. Baraff, et al., "The Optimization of Metal-Insulator-Metal Nonlinear Devices for Use in Multiplexed Liquid Crystal Displays," IEEE Trans. Electron Devices, Vol. ED-28, pp. 736-739 (1981), and S. Morozumi, et al., "Lateral MIM-LCD with 250.times.240 Pixels," Technical Reports of Television Society of Japan (IPD83-8), pp. 39-44, December, 1983.
In addition, an active matrix LCD which uses silicon nitride of small dielectric constant as a nonlinear resistor for MIM element is disclosed in M. Suzuki, et al. "A New Active Diode Matrix LCD Using Off-Stoichiometric SiN.sub.x Layers," Proceedings of the SID, Vol. 28, pp. 101-104 (1987).
An equivalent circuit per pixel of the prior art MIM-LCD is shown in FIG. 1. A liquid crystal element 5 and an MIM element 18 are connected in series between a lead electrode 9 and a transparent counter electrode 15. The MIM element 18 operates as a nonlinear resistor element. When a voltage is applied for a long time between the lead electrode 9 and the transparent counter electrode 15 in order to drive such an MIM-LCD over a long period of time, there occurs a change in the current-voltage (referred to as I-V hereinafter) characteristic as shown in FIG. 2. In FIG. 2, the solid and the broken lines represent the initial characteristic and the characteristic after drive for 10,000 hours, respectively. With such a change in the I-V characteristic, even when a voltage which is the same as that before the change is applied between the lead electrode 9 and the transparent counter electrode 15, the voltage applied to the liquid crystal 5 becomes different from that before the change, and its display characteristic is accordingly changed. This phenomenon is called image sticking.